The present invention relates to testing radiofrequency (RF) wireless packet data signal transceivers, and in particular, to testing such devices having multiple inputs and multiple outputs.
Many of today's electronic devices use wireless technologies for both connectivity and communications purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential of interfering with the operations of one another by virtue of their signal frequencies and power spectral densities, these devices and their wireless technologies must adhere to various wireless technology standard specifications.
When designing such devices, engineers take extraordinary care to ensure that such devices will meet or exceed each of their included wireless technology prescribed standard-based specifications. Furthermore, when these devices are later being manufactured in quantity, they are tested to ensure that manufacturing defects will not cause improper operation, including their adherence to the included wireless technology standard-based specifications.
For testing these devices following their manufacture and assembly, current wireless device test systems (“testers”) employ a subsystem for analyzing signals received from each device. Such subsystems typically include at least a vector signal generator (VSG) for providing the source signals to be transmitted to the device, and a vector signal analyzer (VSA) for analyzing signals produced by the device. The production of test signals by the VSG and signal analyses performed by the VSA are generally programmable so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless technology standards with differing frequency ranges, bandwidths and signal modulation characteristics.
A recent development in the design and operation of wireless radiofrequency (RF) packet data signal transceivers as been the use of multiple inputs and multiple outputs implemented with multiple antennas. In other words, such devices, referred to as multiple-input, multiple-output (MIMO) devices, use multiple antennas for the wireless transmission and reception of their signals. Accordingly, when testing such devices, provisions must be made for testing them in such a way as to exercise their MIMO capabilities. For example, this includes operating the device under test (DUT) such that all of its transmitters and receivers are operating to transmit and receive, respectively, their respective packet data streams via their respective antenna connections. Such complete testing of a N×N (N inputs and N outputs) DUT includes transmitting and receiving data packets via each one of the wireless signal paths (e.g., antenna ports), as well as reducing the number of packet data streams being transmitted and received so as to simulate real world operation in which a packet data stream being conveyed by one or more of the antennas exhibits a null (large attenuation) and thereby prevents its successful reception and transmission to the corresponding device. Conventional test techniques to achieve this have included interrupting, disconnecting or otherwise disabling the transmission and/or reception of one of the wireless signals. However, such a complete reduction in the number of packet data streams being transmitted and received forces the DUT and the device or system with which it is communicating to re-establish their mutual wireless communication link. Such re-establishment of the communication link must be repeated for every transition from one number of packet data streams to another. For example, for a 3×3 DUT to be transitioned from operating with a three-stream (using two transmitters and three or more receivers) communication link (three antennas conveying three received signals and three transmit signals) to two-stream communication link (transmitting and receiving two streams while still using all three transmitters and three receivers) and then to single-stream communication link (where the three transmitters and three receivers use only the single stream) will require, following establishment of the initial communication link, two instances of re-establishing the communication link as the DUT transitions from reception and transmission of three packet data streams to two packet data streams and then to one packet data stream.
Such resetting of the RF signal communication link between the DUT and its communication partner (e.g., a test system including one or more VSGs and VSAs, often referred to as “tester”, or a N×N MIMO reference device, such as a previously tested and proven transceiver of similar design) often takes a significant amount of time as compared to other tasks performed during the testing sequence. Many of such other parts of the other overall testing sequence are not susceptible to being shortened in their durations. Accordingly, it would be desirable to have a technique while testing a MIMO DUT for reducing transmitted and received packet data streams without requiring resetting or re-establishing the communication link.